A paver is a machine by means of which unbonded and bonded layers or pavements can be produced. As soon as a laid pavement is made available for its intended use, subsequent improvements entail substantial efforts, such as the closure of road sections or parts of buildings. Hence, quality control is of great importance in the field of asphalt laying. A system which allows the quality of asphalt laying or the quality of the laid asphalt to be measured is shown in WO 2004/034351 A2. In particular, it is possible to manually check the properties of the asphalt, and, in so doing, individual measurement processes can be linked with site data.
As regards causes, especially the processing temperature of the pavements used in road construction, in particular asphalt, is an important process variable which substantially influences the usage properties, such as stability, layer adhesion and service life of the laid pavements. Pavers typically distribute paving material and execute precompacting of a surface of the paving material with a screed, which is attached to the rear end of the paver and drawn thereby. Subsequently, the laid pavement is compacted still further by rollers. Like other factors, such as environmental and weather conditions during laying, the temperature of the material in different stages of the laying process influences the efficiency and the success of a paving job.
Processing e.g., paving material under optimum temperature conditions has long been recognized as important, but such processing often entails manual control measurements on the part of the support and operating staff. Paving material is typically obtained at a comparatively high temperature at an asphalt or bitumen plant. Depending on the distance a supply machine has to travel so as to reach a work site as well as on the traffic and the ambient temperature, the asphalt may cool to a certain extent prior to delivery. In addition, progress of the paving machines and of the compacting machines or rollers may vary. If the whole paving process has slowed down, haul trucks may sometimes have to wait to offload the paving material. The extent of cooling, once the paving material has finally reached the paving machine, may vary depending on the temperature of the paving material at delivery, environmental factors, the use of insulated or non-insulated haul trucks and proper versus improper operation of the paving machine, etc. Ecological and economical aspects, e.g., with respect to the amount of gas consumed at the burner, become here increasingly important. In some cases, paving material may segregate within the paving machine, and thus relatively cooler and relatively hotter pockets or accumulations of material within the machine may exist, leading to unexpected temperature gradients in the paving material once distributed on the work surface. When the paving material has been discharged and distributed by the paving machine or paver, and subsequently been treated by means of the screed, and is then ready to be compacted still further by the various compacting machines, its temperature can vary significantly from an expected temperature and can be non-uniform in temperature from one paved region to the next due to unintended segregation or poor mixing.
Due to the paramount importance of the laying temperature of the pavement, measuring of the laying temperature becomes increasingly important and, within the last few years, various solutions have been developed on the market, which satisfy the demand for metrological proof of the laying temperature and thus facilitate also subsequent improvements. Various systems which measure for this purpose the laying temperature behind the paver, in particular behind the screed, are commercially available. The available systems range from a pyrometer array to thermal or infrared scanners and also to pivotable pyrometers. These systems are used for obtaining a more or less areal impression of the temperature profile behind the paver.
Other systems for obtaining laying temperature information are based on an infrared camera whose image data are arithmetically converted into scanning lines by means of suitable software. These lines are spaced at a defined distance from the trailing edge of the screed, each line representing the temperature profile of the paved layer transversal to the travelling direction of the paver. The software combines the individual lines so as to form a planar image, a temperature map or two-dimensional temperature profile. These images are subsequently used for assessing the temperature distribution of the laid asphalt. As mentioned above, a temperature distribution having the highest possible uniformity is here a quality characteristic, since this will provide uniform preconditions for subsequent compacting by means of rollers.
DE 10 2008 058 481 A1 describes an evaluation of such a temperature profile during the paving process and, in particular, the adaptation of a paving plan for the use of the individual machines of the paving train. Especially on the basis of the temperature information acquired, the distance between the compacting rollers and the paving machine or paver is adapted such that the asphalt will not be processed by the subsequent compacting rollers within a temperature range known as “tender zone”, i.e., it will be compacted either above the upper limit temperature or below the lower limit temperature of the temperature range of the tender zone.
WO 00/70150 A1, in turn, deals with a temperature monitoring system for use on a paver, said temperature monitoring system scanning the temperature of the laid pavement line by line in a line scan mode. According to respective embodiments, the information obtained is directly used for an adapted control of the screed or communicated to other machines of the paving train.
These known systems proceed from an idealized detection of the temperature of the laid pavement. In practice, however, it is frequently such that rollers or other machines of the paving train enter the pavement or that individual persons of the operating staff cross it. This may lead to incorrect measurements of the laying temperature, which find expression in a two-dimensional temperature profile or temperature map. The then detected local temperature will be discerned as being, in comparison with the temperature of the surrounding laid pavement, either too low, too high, very inhomogeneous, or as deviating in some other way from the ambient temperature, but subsequently it cannot easily be ascertained whether the reason for this deviation is an inhomogeneity in the laid material, caused e.g., by segregation and pocket formation, or a detection of foreign objects. Furthermore, there may be a malfunction of an infrared camera or of a comparable temperature measurement device used for detecting the laying temperature, so that the actual measuring points of temperature detection lie outside the target area of the laid pavement or the detected image area varies incorrectly between the measurements. If the temperature measurement device is not correctly directed onto the laid pavement, the detected temperature may confront the evaluating staff with unsolvable problems.